Oxyhemoglobin and deoxyhemoglobin differentially absorb red and infrared light. An optical oximeter uses the difference in absorption to measure blood oxygen saturation. The difference in absorption can also be used to measure hematocrit, hemoglobin and other parameters of the blood. One method for measuring hematocrit, hemoglobin and oxygen saturation is by passing red light and infrared light through blood in shorter and longer paths and using the differences in light energy remaining to calculate the desired parameters.
For some medical procedures, an extracorporeal circuit with a pump and an oxygenator is used to temporarily replace the function of the heart and lungs, respectively. To maintain proper physiological conditions, the blood's oxygen saturation and hemoglobin concentration are periodically measured by taking blood samples from the circuit and sending the samples to a clinical laboratory. In the above system, the blood parameters are not continuously monitored. This results in delay for treatment of physiological changes that may be identified by measuring oxygen saturation, hemoglobin and hematocrit.
The delay encountered when blood parameters are measured in a clinical laboratory may be eliminated by directly measuring the parameters of blood as it passes through the extracorporeal circuit. Devices which directly measure the parameters irradiate the blood and measure the reflected or transmitted light to calculate the blood parameters. However, these devices unnecessarily add to the complexity of the circuit requiring that additional devices, such as cuvettes, be plumbed into the circuit's conduit. Further, because an apparatus must be plumbed into the circuit, the measurements are taken at a fixed location within the extracorporeal circuit. The operator has no ability to monitor blood parameters at other locations. Also, the splicing of elements into the circuit provides a point for the introduction of pathogens and other contaminants through improper sterilization or during the process of inserting the apparatus into the circuit.
Other types of detectors suffer from further disadvantages. Some detectors require sensors to physically contact the blood in order to measure the intensity of reflected light. These devices suffer from inaccuracy due to changes over time in the detector under the influence of the blood's physical properties. This alters the measurement of the reflected light detected resulting in an inaccurate measurement of the blood's characteristics. Further, there is a risk of electrical leakage from the electric components that could be detrimental to the patient.
The present invention provides an apparatus and method for measuring blood parameters by attaching sensors to the conduit of an extracorporeal circuit. Thus, the present invention provides numerous advantages over prior art devices. For example, the present invention eliminates the need for placing sensors in direct contact with the blood and the need for plumbing additional elements into the extracorporeal circuit. Further, the present invention provides the operator with the flexibility to move the clamp to different locations on the extracorporeal circuit's conduit during an operation (e.g. from the venous to the arterial side of the circuit). Also, since the device does not contact the blood, the clamp does not need to be sterilized and there is no risk of electrical leakage.